FIG. 1 illustrates a simplified example of a RF communication device 100 with multi-band RF communication pipes. The device 100 comprises a mobile communication section with a sending branch 130 and a receiving branch 140, for enabling communication according to certain standards of present mobile communications systems, adapted, for example, to 2G (second generation) technology as GSM (Global System for Mobile Communications) or EDGE (Enhanced Data rates for GSM Evolution), 3G (third-generation) technology as WCDMA (Wideband Code Division Multiple Access) or UMTS (Universal Mobile Telecommunications System), or WLAN (wireless local area network) technology, just to name some present well known technologies.
For that purpose the device 100 comprises a set of antennas 121, 122 connected a signal switch 110. Receiving signals from the antennas 121, 122 are supplied to the receiving section 140, which comprises a filter bank 141 with several RF bandpass filters 1, 2, 3, 4, 5 each frequency pass characteristics fixedly configured for pass through of a specific frequency band as required by the respective mobile communications standard to be received. After the respectively used filter, the filtered receiving signal is forwarded to a RF receiving signal processing section 142 for processing of the receiving signal, e. g. down mixing, demodulation, decoding inter alia, such that information carried by the receiving signal can be provided to a base band section 160 of the device 100 for further and designated use thereof.
In the sending branch 130 are a respective RF sending signal processing section 132 for processing from a base band signal provided from the base band section 160, e.g. be encoding, modulating, up-mixing and so on. After the RF sending signal processing section 132, there is a sending power stage 131 with respective power amplifiers and sending filters. From the sending power stage 131 the sending signals are supplied to the antennas 121, 122 via the signal switch 110 for transmission.
The RF communication device 100 with multi-band RF communication pipes of FIG. 1 further comprises a receiving branch for additional telecommunication broadcastings services becoming more and more available such as TvoM (TV on Mobile) or DVB-T (Digital Video Broadcasting-Terrestrial), which are transmitted in respective frequency bands such as VHF-band, UHF-band, or L-band.
Accordingly, there the device 100 comprises respective configured antennas 123, 124, 125 which designated to a respective RF receiving circuits 151, 152, 153 from which a respective receiving signal is supplied again to respective adapted bandpass filters 6, 7, 8, where each frequency pass characteristics again is fixedly configured for pass through of a specific frequency band. The filtered receiving signal is forwarded to a respective configured RF receiving signal processing section 152, where the receiving signal is processed in order to provide the desired telecommunication signal to the base band section for designated use thereof.
In the example of FIG. 1, at least a total of 8 individual RF bandpass filters 1, 2, 3, . . . , 7, 8 are employed and needed. Accordingly, the conventional approach of FIG. 1 has drawbacks as being costly because each RF bandpass filters 1, 2, 3, . . . , 7, 8 is a stand-alone device. Further, each filter device is not optimized for miniaturization. Furthermore, the filter devices are lossy which makes challenging the respective technical specifications.
A promising approach is application of a so-called a distributed amplifier (DA), a diagram illustrating the function principle is shown in FIG. 2. Accordingly, a DA 200 consists of a pair of transmission lines, namely an input transmission line 210 and an output transmission line 220 both assumed to have a characteristic impedance of Z0. The transmission lines 210, 220 connect independently the inputs and outputs of several active elements T1 to TN, depicted as transistors. When an signal is supplied to the input transmission line 210 connected via the input In of the first active element T1, as the input signal propagates down the input transmission line 210, the individual active elements T1 to TN respond to the forward traveling input signal step by step, thereby inducing an amplified complementary forward traveling output signal on the output transmission line 220. Assumed the delays of the input line sections Sin and output line sections Sout are made equal by appropriate selection of propagation constants and lengths, the output signals from each individual active element T1 to TN are such as to sum in phase. Respective terminating resistors Zg and Zd are used to minimize destructive reflections. The transconductive gain of each element T1 to TN is assumed to be Gm and the output impedance seen by each of the active elements T1 to TN is half the characteristic impedance of the respective transmission line 210 or 220. Hence, the overall voltage gain of the DA 200 can be determined by formula (1).
                              G          =                      N            ·                          G              m                        ·                                          Z                0                            2                                      ,                            (        1        )            where N denotes the number of amplifying stages comprising the active elements T1, T2, T3, T4. If losses may be neglected, the gain of the DA 200 has a linear dependence on the number of amplifying stages. Unlike the multiplicative nature of a cascade of conventional amplifiers, the DA 200 has an additive effect. Hence, the architecture of the DA 200 achieves a synergistic property that provides gain at frequencies beyond that of the unity-gain frequency of the individual stages.
U.S. Pat. No. 6,650,185 shows an application of the distributed amplifier technology in connection with FIG. 2, where the circuit design is such to have a frequency selective amplifier. The disclosed selective amplifier consists of a plurality of amplifier stages that collectively drive a load. The plurality of amplifier stages have input nodes and output nodes, where output phase shift circuits connect the output nodes of the plurality of amplifier stages in a manner that causes output signals from the plurality of output nodes to add together for delivery to the load, wherein the plurality of output phase shift circuits have a plurality of phase shifts. Further, a plurality of input phase shift circuits are coupled to the plurality of input nodes and provide input signals thereto, wherein the plurality of input phase shift circuits have also a plurality of phase shifts. In order to achieve the frequency selectivity of the selective differential amplifier, in U.S. Pat. No. 6,650,185, the phase shifts caused by the input phase shift circuits are not equal to the phase shifts caused by the output phase shift circuits, so that output signals from the plurality of amplifier stages are added with a frequency dependent phase relationship.
A further approach for removing a plurality of required, such as the RF bandpass filters 1, 2, 3, . . . , 7, 8 of device 100 of FIG. 1, is use of active filters, which are based on negative resistance concepts or recursive methods. However, the drawbacks are a quite high noise Figure, a limited tuning range, e.g. less than an octave, inter alia.